Arylene sulfide polymers have become commercially important resins. The products prepared therefrom are finding increasing utility because of their outstanding durability, toughness, inertness, and versatility. Such resins, although having relatively high melting points, are thermoplastic.
The virgin (i.e., substantially linear and uncured) arylene sulfide resins generally have a relatively high melt flow (e.g., about 3000 to about 10,000 grams/10 minutes). For some purposes, such as encapsulation and coating, it is desirable to have arylene sulfide resins with a melt flow greater than about 15,000 grams/10 minutes. However, for other purposes, such as molding, film making and fiber making, the resins should have a melt flow in the range from about 10 to about 3,000 grams/10 minutes. Since virgin arylene sulfide resins generally have a melt flow ranging from about 3000 to about 10,000 grams/10 minutes, if such resins are to be employed in moldings or the making of polymeric films and/or fibers, the virgin resins must have their melt flow values decreased. Conversely, if such polymeric resins are to be employed for the purposes of encapsulation and/or coating, the virgin arylene sulfide resins must have their melt flow values increased.
One conventional method of decreasing the melt flow of virgin arylene sulfide resins, which is synonymous with increasing the virgin resins' molecular weight, is by a process referred to in the industry as "curing". Both, the extent to which the resin is cured and the final melt flow value obtained are controlled depending upon the intended end use of the polymer. One method of curing an arylene sulfide resin is to subject the resin to an elevated temperature below its melting point while in the presence of a gaseous oxidizing atmosphere. This method of curing virgin arylene sulfide resins is generally long and tedious.
It is known that the rate at which a virgin arylene sulfide resin cures is generally proportional to the temperature at which the resin is being cured. Therefore, one method of increasing the rate at which a virgin resin is cured is by employing a higher curing temperature. However, since it is often desirable to maintain the curing temperature below the melting point of the resin, the extent that the temperature may be increased is limited by the specific resin's melting point. Accordingly, it is an object of this invention to provide a process for increasing the rate at which arylene sulfide resins cure without increasing the curing temperature.
Furthermore, it is also desirable to have virgin arylene sulfide resins which are thermally stable in the melt. In other words, it is desirable to have arylene sulfide resins whose melt flow values do not substantially change while the resins are held at a temperature above their melting point for a period of time, such as, for example, during molding and extrusion procedures. Accordingly, another object of this invention is to provide a process for preparing thermally stable arylene sulfide resins.
A further object of this invention is to provide a process to treat arylene sulfide resins to have varying melt flow values to meet specific fields of utility.
Other objects, aspects and advantages of the invention will be apparent to those skilled in the art upon reading the specification and appended claims.